Arsenic-boron compounds and method of inhibiting corrosion therewith



Patented Sept. 10, 1957 ARSENIC-BORON COMPOUNDS AND METHUD F INHIBITINGCORROSION THEREWITH Gilson H. Rohrback, Seattle, Wash., assignor toCrest Research Laboratories, Inc., Seattle, Wash, 21 corporation ofWashington No Drawing. Application May 3, 1954, SerialNo. 427,377

15 Claims. (Cl. 23-44) This invention relates to new arsenicalcompositions and to a method of employing the compositions to inhibitcorrosion. More specifically, the invention pertains to new compounds ofthe elements arsenic and boron and to the use of those compounds ininhibiting corrosion of ferrous metals by aqueous acid solutions,particularly in oil wells.

The best known and most widely used commercial arsenic compound,arsenous oxide or arsenic trioxide (AS203), is characterized by severalproperties which make it diflicult to handle and generallyunsatisfactory for a variety of uses. In the first place, arsenous oxideis extremely dusty and powdery, which means that during any handling orpouring operations great precautons must be taken to prevent theoperators from breathing the powder because of danger of poisoning. Inthe second place, arsenous oxide is only slightly soluble in water andmust be combined with a strong alkali in order to make it soluble inpractical concentrations. Because of the necessity for combiningarsenous oxide with strong alkali, the resulting commercial product issubject to all of the hazards inherent in strong alkalies generally andis otherwise dangerous in that it may not be exposed to an active metal,such as zinc, since deadly arsine gas may then be generated. The dangerinvolved when zinc is exposed to arsenous oxide in alkali solutionsprevents the use of economical and desirable galvanized handlingequipment.

In addition to arsenous oxide, there exist other commercial arseniccompounds one of the most important of which is sodium arsenite (NaAsOz)which is soluble in water but is caustic. It is, therefore, subject tothe dangers inherent in strong alkalies and to the dangers involved whenplaced in contact with active metals such as zinc. Sodium arsenite isalso highly dusty and powdery, and the dust is easily assimilated by thehuman body thus greatly increasing the handling hazards. A furthercommercial arsenic compound is arsenic chloride (ASCls), but thiscompound is so dangerous that its use has been extremely limited.

One important commercial use of arsenous oxide is in the inhibition ofcorrosion of ferrous metal surfaces exposed to aqeuous acid solutionssuch as are present in oil wells. To be sufficiently soluble for thisuse, the arsenous oxide must be mixed with a strong alkali such assodium hydroxide, a solution of arsenous oxide in aqueous sodiumhydroxide (sodium arsenite) being introduced into the well through theannulus between the well casing and tubing. As the solution thusintroduced falls through the annulus it encounters the carbon dioxidegas naturally present in the well, and the carbon dioxide gas isabsorbed by the water in the inhibitor solution toform carbonic acid.The carbonic acid then neutralizes the sodium hydroxide and results inthe precipitation of arsenous oxide, a poisonous paste or scum, on thecasing and tubing. This process of precipitation is recognized to occurbecause sodium arsenite is stable only in highly basic solutions andtherefore decomposes to form insoluble arsenous oxide as the base isneutralized by carbonic acid. The described precipitation has two highlydetrimental effects, the first ofiwhich is that the poisonous recipitateis a hazard to personnel handling the tubing during maintenance work,and the second of which is that the arsenous oxide thus precipitated isineffective to prevent corrosion and thus is wasted.

In view of the above factors characteristic of commercial arseniccompounds in general, and the use of arsenous oxide in inhibitingcorrosion in particular, it is an object of the present invention toprovide new arsenical compounds which are easy to handle safely, whichare simple and inexpensive to manufacture, and which are highly solublein water to produce essentially neutral solutions free from thecharacteristic of precipitating arsenous oxide.

Another object of the invention is to provide new arsenical compoundswhich in solid form are crystalline in character instead of dusty orpowdery, so that no poisonous dust is raised into the air duringhandling and pouring operations.

A further object of the invention is to provide arsenic compounds whichin aqueous solution are essentially neutral instead of stronglyalkaline, so that none of the dangers inherent in alkalies are presentand no dangerous reactions occur when aqueous solutions of the compoundsare used or stored in galvanized containers, or otherwise exposed toactive metals.

A further object is to provide novel arsenical compounds which areefiiective inhibitors of corrosion of ferrous metal surfaces by aqueousacid solutions, and whose solubilities are not reduced by exposure tocarbon dioxide or to carbonic acid.

A further object of the invention is to provide a method of inhibitingcorrosion of ferrous metal surfaces ex posed to aqueous acid solutions,and specifically to a method of inhibiting corrosion of ferrous metaloil well equipment without causing precipitation of arsenous oxide ontothe equipment.

The and other objects and advantages of the invention will be more fullyset forth in the following specification and claims setting forth thecompounds of the invention and the method of inhibiting corrosion.

Stated generally, the new compounds comprise chemical combinations ofarsenous oxide and a borate in a molar ratio which will give theequivalent of one arsenic atom to one boron atom in the new compounds.Where tetraborate is employed, the molar ratio between arsenous oxideand tetraborate is two to one, respectively. The borate is a borate ofan alkali metal or ammonium. Borates of sodium and ammonium arepreferred since these borates are relatively inexpensive and theresulting compounds are highly soluble in water. Potassium borate isalso preferred but is of lesser value for certain applications since theresulting compound, although many times more soluble than arsenousoxide, is less soluble than compounds prepared with the borates ofsodium and ammonium.

According to a more specific definition, the new compounds may be statedto have the general formula XYB407'2AS203, where both X and Y arematerials selected from a group consisting of the alkali metals andammonium. The materials may be similar, for example Naz, or dissimilar,for example NaK. The symbol XY thus represents one of the followingcombinations: Naz, K2, Liz, (NH4)2, NaK, NaLi, NZNHI, KLi, KNHi, LiNHr.Where the materials are similar, the formula may also be writtenX2B4O'1'2As2O3.

A first preferred compound may be formed by dissolving sodiumtetraborate (Naz'B4O7) and arsenous oxide 3 (AszOa) inwater, andin themolar ratio of one to two, the resulting. compound having theflformulaarsenous oxide is present over the molar ratio of'oneto two, and thesalts are. dissolved in hot water, the excess borax or arsenous oxidewill precipitate out after the solution is cooledexcept for the smallamount of excess arsenous oxide :orborax which would be itself soluble:

in cold water.

Fromthe water solution of:the compound a crystalline precipitate or -trihydrate'having the formula- Na2B4O7 2As203 3H2O may be-formecl byintroduction of a suitable water miscible organicsolvent such as acetoneor dioxane, the precipitate being separated by filtering or draining.Essentially complete precipitation of the compound is assured .by theaddition-of four volumes of organic solvent to one volume of the watersolution containing the compound Na2B4O'1-2As2O3.

When precipitation of the newcompoundis'efiected with certain solvents,the resultingsolid is one in which all or part of the'hydrate water isreplaced by molecules of the solvent itself. Thesolid' compound may beformed decomposition occurs, although experiments haveindi cated thatthe sodium is present in ionizabl'e form so thatit may be replaced byother cationic species. The

ionequation isbelieved to be. as follows:

With relation to the high solid content-of theagueous solution,:.more.=.th'an fifty :zprcent: of th'e compound 'remains' in solutin-, atten, degrees. centigrade; This is-tobecompared with k the. solubilitiesof c the constituent compo n h mselv s .since- ;a,t; ,ten:degrees.centigr.ade l: only; 1.6,:percentof NazB4On 101-120, J and ,only;.1.5 .7percentuof. AS203, will remain in solution in water, 'An important.feature of the aqueous solution is its relative neutrality,

it havinga pH;of.7 .9.. It followsthat the ,aqueoussolue tion of the,new compound will not; react. with active metal such as zinc to producearsinegas, andthat there will'be relatively little danger inhandlingthe,compound.., The properties or. characteristics of the compound inits-hydrate or solid form. include its crystalline ch'ar-.

With-relation to the stability ofthe comsodium borate or arsenous oxide;this beingaccomplished '4. borate compound, a water solution preparedfrom sodium tetraborate and arsenous-oxide, ina -molar ratio of onetotwo, respectively, was used as the sourceof the.crystalline precipitateNa2B4O7-2As2Os-3HzO, precipitation occurring upon addition of dioxane asabove indicated.

The precipitate was redissolved'ain water, re-precipitated v p and driedin air at 110 degrees centigrade. .It was determined that the newprecipitate didnotcontain either= by tests of the physical propertiestoshow, for example, that theprecipitate: was;;easi;l-y .and highlyjsoluble; in cold'water and was stable above 350,.degrees1centigrade. Thenew precipitate. was analyzed for arsenic by the arsenous trisulphidemethodiimaccordance with the procedure described in Scotts' StandardsMethods of .Chemical Analysis, ,fifth edition,: volume. l,-.page 96. Theboron content Was determined by titration according to the methoddescribed in ,Analytical Chemistry. 22,, 697 (1950). It was. found that30.9.- percent boron. was; present as NH2B407,andithat'61-.2.percentarsenic was present as AszOa, thelcombinedpercentages. being 92.1. percent which leaves 7.9 percent for water ofcrystallization. V

Comparison of determined and calculated percentages forNa2B4Ov-2AszO3-3H20 are as follows:

Calculated From Formula 1 Experimentally D termined :ozoco wow: 7

The compound having the formula NazB-rQrZAszOs -.3H2.0. 7

itmay be seen that the formula-ofjthe. trihydrate.,

Na2B 10'z 2As20 7 3H2'Of is correct to within normal limits curacy.

of experimental 'aci The following 1 is 1 a: specific example-of-'-'the-preparat-ion of thedisodium-arseno-borate compound which isformed;

'as stated above, by. dissolving:borax- (sodium tetraborate) l and.arsenous oxidein water and'in} the molar-ratioaof one to two,respectively. 19.8 'gramsmflarsenous-oxide= and 19.1 grams of NazBgOv10H2O were dissolvedin 65 grams. of' water. The solids..went-intosolution uponacter; similar to table salt," as distinguishedfrompowder which is the form of common commercial arsenic compounds such asarsenous'oxideand-sodiumarsenite. Be

causeit is crystalline instead of powdery-in character there is little'danger that the solid Will'pass into the air 7 during handling, whereitcould'be breathed with'consequentdanger; of poisoning. That -the solidform of:the disodium arseno-borate compound is .stable is evidenced by.the fact that it has becmheated fora. periodgof'several hours at'350degreescentigrade withoutsigns of :dec0m xide whichsublinres.at,315..degrees,centigrade,

.Pfoceedinanex io th ..analy i flhedis m ars noa boiling for severalminutes. The solid-i compound was then: formed both by evaporation -andby precipitation-' with a water miscible organicsolvent-asdescribedhere" tofore.

As asecond method of forming-=the --disodium-;arseno borate compound;and which maybetermed-theindiiect method as distinguished from thedi-rect method stated aboxe, arsenous oxide is firstdissolved*inan-equalmolar' ratio of aqueous sodium hydroxide: Boricacid is:then*-addedLin'a-molarratio to the arsenous oxide of- 2"to* 1- and-solutionagainachieved. This reaction-may berep resented by thefollowingequation-f As a specific example .of: the indirect method;19.8", grams of arsenous oxide and14Jgrams of'sodiumhydroxide weremixed. in 100 grams ofgwater, and. the mixture-boiled?" untilthe solidsdissolved. 12, 4:-gramsuof boric. acidswereg.

, then: added and thesolution; boiled..until;clear;; From:

this solution, Nazl3grOr2AszOa was precipitated byq both fihaabove.describe me had a a The second preferred compound formed bycombining tetraborate and arsenous oxide in the molar ratio of one totwo contains ammonium, arsenic and boron and has the formula(NI-I4)2B4O7'2AS2O3, with varying numbers of water molecules. Thisammonium compound,

which may be termed diammonium arseno-borate, may

also be formed both by direct and indirect methods. In the direct methodthe compound is formed by dissolving arsenous oxide in a water solutionof ammonium tetraborate, the molar ratio being two to one. Morespecifically, a solution of (NH4)2B4O7 was first prepared by dissolving24.74 grams of HsBOa in 35 cubic centimeters of 15 N NI-la solutiondiluted to 100 cubic centimeters. This resulted in a solution of(NH4)2B4O7 plus excess NHa. The excess NH3 was removed by boiling, and3956 grams of AS203 were added with stirring and heating until a clearsolution resulted. A hydrate of the compound (NHQzBtOrZASzOs wasprepared from the above solution by the addition of dioxane. In theindirect method, one mole of arsenous oxide is first dissolved in anamount of ammonium hydroxide in excess of two moles, the excess beingrequired because considerable ammonia is lost during solution of thearsenous oxide. Boric acid is then added in a molar ratio to thearsenous oxide of two to one, and the solution stirred at 70 degreescentigrade until solution is achieved. As a specific example of theindirect method, 39.56 grams of AS203 were stirred into a solution of 35cubic centimeters of 15 N NH3 dissolved in 55 cubic centimeters ofwater. The mixture was heated to 70 degrees centigrade and all solidsdissolved. At this temperature 24.74 grams of H3BO3 were slowly addedand stirred until dissolved. From this solution (NI-I4)2B4O7-2As2O3 wasprecipitated by addition of dioxane.

The diammonium arseno-borate compound is many times more soluble inwater than are either ammonium tetraborate or arsenous oxide.Furthermore, the ammonium compound, in its solid form, has been found tobe stable above 350 degrees centigrade whereas ammonium tetraboratemelts below 100 degrees centigrade and arsenous oxide sublimes at 315degrees centigrade. As an additional test to show that diammoniumarseno-borate is a true compound instead of a mere mixture or complex, 1gram of arsenous oxide was mixed into 30 cubic centimeters ofconcentrated water solution of and the mixture was boiled until clear.Thereafter the liquid was cooled until a precipitate'formed and theprecipitate was filtered out. The precipitate was shown to be arsenousoxide and weighed 1.0 plus or minus 0.005 grams. Thus, the amount ofprecipitate. was exactly the same as the amount of arsenous oxide added,which shows that the molar ratio of one tetraborate to two arsenousoxide is critical.

A third preferred compound formed by combining tetraborate and arsenousoxide in the molar ratio of one to two contains the elements potassium,boron and arsenic and has the formula K2B4O7-2AszO3, various numbers ofwater molecules being present when the compound is in its solid form.The dipotassium arseno-borate compound may be prepared both by thedirect and indirect methods as in the case of the ammonium and sodiumcompounds. According to the direct method, KzBrOv-IOHzO (potassiumtetraborate, decahydrate) and AS203 are boiled together in the molarratio of one to two, respectively. As a specific example, 32.36 grams ofKzBrOv-IOHzO and 39.56 grams of AS203 were boiled together, whilestirring, in 100 cubic centimeters of water until a clear solutionresulted.

According to the indirect method, 2 moles of AS203 are dissolved in aWater solution containing 2 moles of KOH. Four moles of HsBOs are thenadded and the solution boiled until clear. More specifically, 39.56grams of A8203 were dissolved, by boiling and stirring, in

100 cubic centimeters of water in which was previously dissolved 6.60grams of percent commercial KOH. To this solution were added 24.74 gramsof I-lsBOa and the mixture was heated with stirring until dissolved.

A hydrate of the salt KZB40'I'ZAS203 can be prepared from the abovesolutions, formed both by the direct and indirect methods, by adding anorganic liquid solvent such as dioxane, and also by evaporation.Moreover, the potassium salt has been found to have a rapidly decreasingsolubility with decreasing temperature and may therefore be precipitatedby cooling to 10 degrees centigrade at which temperature the salt willprecipitate on standing.

The dipotassium arseno-borate compound was tested, as described above inconnection with the ammonium salt, and similar results were found. Thus,the

compound is many times more soluble in water than are simple mixtures,and in its solid form is stable above 350 degrees centigrade, whereaspotassium tetraborate melts at degrees centigrade and arsenous oxidesublimes at 315 degrees centigrade. The potassium compound was alsotested, as described above in connection with the ammonium compound, bydissolving one gram of arsenous oxide in a water solution of thecompound, and then precipitating to recover the gram.

In addition to the pure salts such as disodium arsenoborate, dipotassiumarseno-borate, and diammonium arseno-borate, it is possible to formmixed salts as indicated heretofore. One such mixed salt is sodiumpotassium arseno-borate (NaKBrOq-ZAszOs) and may be formed by addingdioxane or similar organic solvent to a water solution containing boththe sodium and potassium arsenoborates. The resulting precipitate willthen comprise not only the pure salts but also a substantial amount ofthe mixed salt. As a specific example, 19.8 grams of arsenous oxide, 2grams of sodium hydroxide, and 2.8 grams of potassium hydroxide weremixed in 100 grams of water and the mixture boiled until the solidsdissolved. 12.4 grams of boric acid were then added and the solutionboiled until clear. From this solution NaKB4Ov-2AS2O3, NazBeOrZAszOs,and K2B4Ov-2As2Os were precipitated by addition of dioxane.

Although the new arseno-borate compounds have been described above ashaving the general formula XYB4072AS203, it is a fact that since truecompounds are formed the formula may also be written XYB4As4013, whereXY represents Naz, K2, (NHtlg, etc. Thus, disodium arseno-borate wouldhave the formula Na2B4As-iO13, diammonium arseno-borate the formula(NI-I4)2B4AS401s, and dipotassium arseno-borate the formula K2B4AS4Q13.

It is of importance that the compounds are chemical combinations ofboron oxide and arsenous oxide, in addition to being chemicalcombinations of borate and arsenous oxide as previously stated. Just assodium tetraborate (NazBrOq), for example, may also be writtenNazO-ZBzOs, disodium arseno-borate may be represented by the formulaNazO-ZBaOa-ZAszOa. The described arseno-borate compounds are thereforeseen to be chemical combination of boron oxide and arsenous oxide inequimolecular quantities, in combination with the basic oxides NazO,K20, and (NHQzO (theoretical).

It is contemplated that the new compounds will have substantialcommercial application in a wide number of fields including the field ofagricultural chemistry, and more particularly in the killing of insects,rodents, and weeds. It has already been found that disodium arsenoborateproduces lethal results when applied to rodents and certain weeds. Theuse of the compounds in inhibiting corrosion of ferrous metal surfacesby aqueous acid solutions, particularly in oil wells, is of greatimportance and is set forth in detail below.

7 Workers.

'In many oil fields the production of fluids from the subsurfaceformation is accompanied by severe corrosion tion of soluble ferroussalts. In such oil fieldsit isnecessary to make frequent costlyreplacement of equipment that has failed as a result of the corrosion.As stated above, this corrosive action has been mitigated by introducingintothe well a solution of arsenous oxide in aque ous alkali but thispractice hasfrequently resulted, particularly in Wells having asubstantial production of carbon dioxide gas, in precipitation of thearsenous oxide onto the casing and tubing where it is useless inpreventing corrosion and is a substantial menace to the oil fieldAccording to the present invention, the corrosion is mitigated byintroducing into the well a composition of matter containing boron andarsenic, and more particularly arsenous oxide and a bor ate.Specifically, the inhibitor introduced into the well isacompound setforth in detail above and formed by combining arsenous oxide andtetrahorate in 'the molar ratio of two to one. The compoundNa'2B4O'1-2AszO and the compound (NH4)2B4O'1-2As2O3 are preferred sincethese compounds have high solubilities at normal temperature and willnot come out of the aqueous solution when introduced into the well,regardless of the amount of carbon dioxide present. K2B4O7-2A's2O3 isalso satisfactory in some wells but is of lesser'value since it isrelatively insoluble as compared to the sodium or ammonium compounds.

The inhibitor is preferably introduced in' liquid form,

.and in various ways depending on the physical setup at a given well.One convenient method is to pump continuously a solution of theinhibitor into the open annular space between the producing tubing andthe casing. Another method is to lubricate larger quantities of theinhibitor periodically into the well annulus. The liquid can also bepumped directly into the tubing and forced down the well into'theformation where it will be returned'slowly over a long time period withthe produced well fluid.

A preferred inhibitor solution comprises two pounds of Na2B4O7'2As2O3dissolved in one gallon of water and having a pH of 7.9. A secondpreferred solution comprises three pounds of (NH4)2B4O7-2As2Os dissolvedin one gallon of water and having a pH of 7.9. These solutions arediluted with Water and introduced into the well for the purpose ofinhibiting. corrosion of ferrous metal surfaces, the. additional waterbeing utilized for thepurpose of washing the solution to the wellbottom.

The amount of inhibitor introduced is such that the Water produced bythe well will have an inhibitor concentration (calculated as the newcompound) of from 1 to l parts per million (p. p. m.). Preferably, thecoucentration is approximately 20 parts per million since thisconcentration produces substantially complete corrosion inhibition withbut a small amount of inhibitor.

The effectiveness of the inhibitor has been tested in the laboratory byusing a salt solution or brine containing 30 grams of NaCl per liter ofwater. This brine 'Was'saturated with carbon dioxide to remove oxygenand to give the solution on acidity representative of that found in oilwells. The carbon dioxide saturated brine was heated to 170 degreesFahrenheit and flowed at a slow rate past cylinders or coupons of SAE1020 steel. A measure ment of the evolved hydrogen was used to determinethe corrosion'rate of the steel coupons. 7 i

The following table gives the percent of corrosion inhibition fordifferent concentrations of N212B4O7-2AszO3, (NH4)2B4O7'2AszO3, andK;2B407;2AS2Q3'I1 the brine.

' Coneentra- I Percent tion Inhibi- (p. p. m.) tion -2 NMB407 A5193 7 n1 20 96 g i t 50 1% K2B407'2AS20 7 g nnmnlorzaslo u g Thepercentageinhibition was calculated relative to the corrosion rate when noinhibitor was pre'sent.

According tothe best understanding of the inventor,

the corrosion inhibition effect is produced by the anion 4 '1-2Asz sl"ich r su ts. fr m oniz i nof; h compounds. as previously indicated.This. anion is reduced, y a a node-re c ion i h Well. to orm sen and b rc addithenidaflic a s nic b inap tedo th ferrous metal surfa es to prouc e P otec iv f e t- The q ation f r this athqd rea m y be pr n asfollows: V I

The above equation indicates that the anion breaks down into metallicarsenic. ,without any intermediate step in which arsenous oxide isproduced.

In addition to. the preferred method of introducing ried out by mixingborax and arsenous oxide, for .ex-.

ample, in powderor stick form and introducing them into the Well, areaction then occurring when the water naturally p'resentin the well isencountered. Stated'other wise, although the inhibitor i s--preferab1yintroduced in reacted form (the new compounds it may in some instancesbe introduced in the form of ingredients which naturally present in thewell when dissolved in the water will form the, new, compounds.

While the particular composition of matter and method herein describedin detail'are-fully capable of attaining the objects and providipgrtheadvantages hereinbefore stated, it is to be understood. that theyare merely illus; trative of the presently preferred embodiments of theinventionand'that no limitations are intended otherthan as defined inthe appended claims.

aim: U ,7 '1. 'A new chemical compound represented by the foru a.=" L.XYB'4O7'2As2O3 WhereinX and Y are .cationsselected'fromp group consisting of the alkali metals-and ammonium.

2. A new chemical compound represented by the formula:

' X2'B4O'1-2As2'Q V wherein Xis acajtionlselected from a groupconsisting of the alkali metals ,andiammonium.

,3. A new chemical compoundrepresented by the formulajNezB40'l 2AszO o4. An w chemical compound re resented by the formula K2B4O7v2As2O3, V

A n w. chemi al-compound p se t d by the f mu a (N EBtOv-Z sZQBQ' 1 6.An inhibitor of acid attack on ferrousmfital 'surby the formulaz. i l

" X .B-iQ'r2.4 293v 5 wher n and Ye-re ions. selecte from a -gro pconsisting o helial s li meta and ammoni m- 9 7. An inhibitor of acidattack on ferrous metal surfaces, comprising a new chemical compoundrepresented by the formula:

X2B40'z'2As20s wherein X is a cation selected from a group consisting ofthe alkali metals and ammonium.

8. An inhibitor of acid attack on ferrous metal surfaces, comprising achemical compound having the formula NazBsOr 2AS203.

9. An inhibitor of acid attack on ferrous metal surfaces, comprising achemical compound having the formula (NHi) 2B4O'z 2As2O3.

10. An inhibitor of acid attack on ferrous metal surfaces, comprising achemical compound having the formula K2B4O'1-2AS2O3.

11. A method of inhibiting the corrosion of ferrous metal surfaces in anoil well delivering a well fluid comprising oil, brine and carbondioxide gas, which comprises introducing into the well bottom in aconcentration effective to inhibit corrosion of ferrous metal surfacesan inhibitor containing a chemical compound represented by the formula:

wherein X and Y are cations selected from a group consisting of thealkali metals and ammonium.

12. A method of inhibiting the corrision of ferrous metal surfaces in anoil well delivering a well fluid comprising oil, brine and carbondioxide gas, which comprises introducing into the well bottom in aconcentration effective to inhibit corrosion of ferrous metal surfacesan inhibitor containing a new chemical compound represented by theformula:

wherein X is a cation selected from a group consisting of the alkalimetals and ammonium.

13. A method of inhibiting the corrosion of ferrous metal surfaces in anoil well delivering a well fluid comprising oil, brine and carbondioxide gas, which comprises introducing into the well bottom aninhibitor compound having the formula NazBsOq-ZAsaOa, said compoundbeing introduced in an amount sufficient to give the produced water aninhibitor concentration of 1 to p. p. m.

14. A method of inhibiting the corrosion of ferrous metal surfaces in anoil well delivering a Well fluid comprising oil, brine and carbondioxide gas, which comprises introducing into the well bottom aninhibitor compound having the formula (NH4)2B4O-z-2As2Oa, said compoundbeing introduced in an amount sufficient to give the produced water aninhibitor concentration of 1 to 100 p. p. m.

15. A method of inhibiting the corrosion of ferrous metal surfaces in anoil Well delivering a Well fluid comprising oil, brine and carbondioxide gas, which comprises introducing into the well bottom aninhibitor compound having the formula K2B4O7-2As2Oa, said compound beingintroduced in an amount sufficient to give the produced water aninhibitor concentration of l to 100 p. p. m.

References Cited in the file of this patent UNITED STATES PATENTS1,446,160 Cullen Feb. 20, 1923 2,094,881 Gale Oct. 5, 1937 2,096,266Suhr Oct. 19, 1937 2,319,777 Le Duc May 25, 1943 2,596,425 Moyer et a1.May 13, 1952 2,607,744 Viles Aug. 19, 1952 OTHER REFERENCES Mellor: AComprehensive Treatise on Inorganic and Theoretical Chemistry, vol. 5,page 107.

Gmelin-Kraut: Handbuch der Anorganischen Chemie, vol. 3.2, page 511.

7. AN INHIBITOR OF ACID ATTACK AN FERROUS METAL SURFACES, COMPRISING ANEW CHEMICAL COMPOUND REPRESENTED BY THE FORMULA: